DE 2 751 116 discloses a testing arrangement for testing vehicle lighting circuits. Constant current sources are switched so as to supply currents depending on the expected load to different lighting circuits. The voltages across the lighting circuits are measured and a fault is indicated if the voltage is higher than a preset expected value. This arrangement therefore detects bulb failure in such lighting circuits.
DE 3 842 921 discloses an arrangement for monitoring the currents drawn by electrical loads. The load current is measured by switching a current sensing resistor into the load circuit and measuring the voltage across the resistor. This voltage is compared with a threshold which indicates whether the load current is acceptable.
DE 4 338 462 discloses a control system for electrical consumers in a motor vehicle. Power is applied to the electrical consumers via a constant current source while switching off the battery voltage for a short time. The voltage across the consumer is monitored and a fault is indicated if it has an unacceptable value during the short time when the constant current source is connected in place of the battery voltage.